Plant disease caused by pathogens such as fungi are a significant economic cost to plant-based industries. Losses may arise through spoilage of produce both pre- and post-harvest, loss of plants themselves or through reduction in growth and fruiting abilities.
Traditionally, control of plant pathogens has been pursued through the application of chemicals such as fungicides. The use of chemicals is subject to a number of disadvantages. The pathogens can and have developed tolerance to chemicals over time, producing fungicide resistant populations. Chemical residues may also pose environmental hazards as well as raising health concerns.
The problem is particularly illustrated in the grape and wine industries. Bunch rot of grapes, caused by the fungus Botrytis cinerea, is estimated to cause losses of $18 million dollars per annum to the New Zealand wine industry alone. Botrytis control has been by way of fungicides. The practice is unsustainable because fungicide resistance is widespread in many vineyards and there is consumer pressure for reduction in pesticide residue.
Biological control presents an alternative means of controlling plant disease which is potentially more effective and specific than current methods, as well as reducing dependence on chemicals. Such biological control methods are perceived as a “natural” alternative to fungicides with the advantage of greater public acceptance, reduced environmental contamination and increased sustainability.
Mechanisms of biological control are diverse. One mechanism which has been demonstrated to be effective is the use of antagonist microorganisms such as bacteria, yeast and fungi to control plant disease.
Biological control of phytopathogenic fungi such as Botrytis cinerea, with selected biological control agents (BCAs) was reported by Wood in 1951 and later by Newhook in 1957 using the BCA fungus Cladosporium cladosporiodes. The introduction at that time of cheap, effective and easy to apply fungicides halted any further development of BCAs. More recently, other antagonistic microorganisms for use in biological control of plant disease have been identified.
The use of Ulocladium atrum to control botrytis in a range of plants has been proposed, for example for: Botrytis in onions (Köhl et al, 1995b), botrytis in lilies (Köhl et al, 1995a, Elmer & Köhl, 1998), botrytis in cyclamen (Köhl et al, 1998), and botrytis in grapes (Schoene et al, 1999). However, there are also reports of pathogenicity to some plant species exhibited by U. atrum (Butler et al. 1979).
The efficacy of various Ulocladium spp. such as Ulocladium atrum as biological control agents, has also been discussed by Elmer et al, 1995; Walter et al, 1996a,b; Boyd-Wilson et al, 1998; Reglinski et al, 1999, 2000, Hill et al, 1998, Vanneste et al, 1999, Michailides & Elmer, 2000.
It will therefore be appreciated that the Ulocladium species clearly considered as prime candidates for effective BCAs have been extensively researched over the past decade. However, to date none of the candidates have proved ideal, either due to plant pathogenicity concerns or through failure to quickly establish on the target plant plus survive the environmental variability existing in the field.
Surprisingly, the applicants have now identified a Ulocladium species not mentioned in any of the earlier reports as an effective BCA. The applicants have determined that this species, Ulocladium oudemansii, is highly effective in controlling saprophytic fungi such as botrytis and successfully establishing in plant tissues in the field. Moreover, to date there are no records of U. oudemansii causing disease in plants or plant products.
It is therefore an object of the present invention to provide a biological control composition comprising at least one strain of Ulocladium oudemansii effective against a Botrytis species, or at least to provide the public with a useful choice.